Cicek Muzaffer, Fukuyama Ryuichi, Welch Danny R, Sizemore Nywana, Casey Graham
Department of Cancer Biology, Lerner Research Institute, Cleveland Clinic Lerner School of Medicine, Cleveland, Ohio 44195, USA.
Cancer Res. 2005 May 1;65(9):3586-95. doi: 10.1158/0008-5472.CAN-04-3139.
Breast cancer metastasis suppressor 1 (BRMS1) functions as a metastasis suppressor gene in breast cancer and melanoma cell lines, but the mechanism of BRMS1 suppression remains unclear. We determined that BRMS1 expression was inversely correlated with that of urokinase-type plasminogen activator (uPA), a prometastatic gene that is regulated at least in part by nuclear factor-kappaB (NF-kappaB). To further investigate the role of NF-kappaB in BRMS1-regulated gene expression, we examined NF-kappaB binding activity and found an inverse correlation between BRMS1 expression and NF-kappaB binding activity in MDA-MB-231 breast cancer and C8161.9 melanoma cells stably expressing BRMS1. In contrast, BRMS1 expression had no effect on activation of the activator protein-1 transcription factor. Further, we showed that suppression of both constitutive and tumor necrosis factor-alpha-induced NF-kappaB activation by BRMS1 may be due to inhibition of IkappaBalpha phosphorylation and degradation. To examine the relationship between BRMS1 and uPA expression in primary breast tumors, we screened a breast cancer dot blot array of normalized cDNA from 50 breast tumors and corresponding normal breast tissues. There was a significant reduction in BRMS1 mRNA expression in breast tumors compared with matched normal breast tissues (paired t test, P < 0.0001) and a general inverse correlation with uPA gene expression (P < 0.01). These results suggest that at least one of the underlying mechanisms of BRMS1-dependent suppression of tumor metastasis includes inhibition of NF-kappaB activity and subsequent suppression of uPA expression in breast cancer and melanoma cells.
乳腺癌转移抑制因子1（BRMS1）在乳腺癌和黑色素瘤细胞系中作为一种转移抑制基因发挥作用，但其抑制机制尚不清楚。我们确定BRMS1的表达与尿激酶型纤溶酶原激活剂（uPA）呈负相关，uPA是一种促转移基因，至少部分受核因子-κB（NF-κB）调控。为了进一步研究NF-κB在BRMS1调控的基因表达中的作用，我们检测了NF-κB的结合活性，发现在稳定表达BRMS1的MDA-MB-231乳腺癌细胞和C8161.9黑色素瘤细胞中，BRMS1表达与NF-κB结合活性呈负相关。相反，BRMS1表达对激活蛋白-1转录因子的激活没有影响。此外，我们表明BRMS1对组成型和肿瘤坏死因子-α诱导的NF-κB激活的抑制可能是由于对IκBα磷酸化和降解的抑制。为了研究原发性乳腺肿瘤中BRMS1与uPA表达之间的关系，我们筛选了来自50个乳腺肿瘤及相应正常乳腺组织的标准化cDNA的乳腺癌点杂交阵列。与匹配的正常乳腺组织相比，乳腺肿瘤中BRMS1 mRNA表达显著降低（配对t检验，P<0.0001），且与uPA基因表达总体呈负相关（P<0.01）。这些结果表明，BRMS1依赖的肿瘤转移抑制的潜在机制中至少有一种包括抑制乳腺癌和黑色素瘤细胞中的NF-κB活性以及随后抑制uPA表达。
